Engine safety system having safety assembly indentifiably operable for each combustion chamber

ABSTRACT

The safety system is for internal combustion engines, especially snowmobiles, having at least two combustion chambers; each combustion chamber is equipped with a safety assembly operable independently of the others. Each individual safety assembly includes a temperature sensor which is so mounted as to sense an unsafe operating temperature for the specific combustion chamber with which it is arranged. Preferred mounting of the sensor is at the exhaust port for the combustion chamber, or alternately in a position for reading temperatures from the base brass or copper gasket for the spark plug. In the preferred embodiment, the sensor automatically actuates a responsive switch means when unsafe operating temperatures are reached; and this serves to interrupt temporarily the intermittent electrical actuation of the ignition means or spark plug for the combustion chamber. The interruption lasts for the time the chamber is at the unsafe temperature. When the chamber returns to a safe temperature, the switch automatically serves to reinstate the intermittent electrical actuation of the spark means for it. Additionally, however, a separate manually-operated switch permits negation of the effect of the automatic interruption so as to reinstate spark ignition even when the individual combustion chamber is at the unsafe temperature. In an alternate embodiment, the temperature sensor actuates a responsive warning when an unsafe operating temperature for the chamber is reached. The warning may be such as to illuminate an instrument panel light or cause an audible sound (such as a buzzer) for the chamber. Thereafter, a manually-operated switch controlled by an operator may be shifted to terminate or interrupt temporarily the intermittent electrical actuation of the ignition means for the specific over-heated chamber.

Unitedv States Patent [191 Boldt [111 3,760,781 [451 Sept. 25, 1973 ENGINE SAFETY SYSTEM HAVING SAFETY ASSEMBLY INDENTIFIABLY OPERABLE FOR EACH COMBUSTION CHAMBER [76] Inventor: Glen R. Boldt, RR. 2, Baldwin, Wis. 54002 v [22] Filed: Mar.,26, 1971 [21] App]. No.: 128,323

U.S. Cl.

i 123/148 S, 123/198 DC [51] Int..Cl..'...- F02p 11/02, F02p. 11/06 [58]. Field of,Search...-.....,......... 123/198 DC, 148 S, 123/148 A, 198 F, 146.5 D

[56] References Cited UNITED STATES PATENTS 2,010,960 8/1935 Pogue 123/198 DC 3,656,101 4/1972 Akeley... 123/198 DC 2,231,845 2/1941 Curran 123/198 DC 2,509,400 5/1950 Roswell 123/198 DC 1,854,571 4/1932 Albertson... 123/198 DC 2,131,264 9/1938 Benjamin 123/198 DC 2,410,998 11/1946 Reauls 123/198 DC 2,699,161 1/1955 Pees 123/198 DC 2,930,365 3/1960 Muscato 123/198 DC Primary Examiner-Laurence M. Goodridge Assistant Examiner-Dennis Toth Attorney-Robert C. Baker [57] ABSTRACT The safety system is for internal combustion engines, especially snowmobiles, having at least two combustion chambers; each combustion chamber is equipped with a safety assembly operable independently of the/others. v

Each individual safety assembly includes a temperature sensor which is so mounted as to sense an unsafe operating temperature for the specific combustion chamber with which it is arranged. Preferred mounting of the sensor is at the exhaust port for the combustion chamber, or alternately in a position for reading temperatures from the base brass or copper gasket for thespark plug. In the preferred embodiment, the sensor automatically actuates a responsive switch means when unsafe operating temperatures are reached; and this serves to interrupt temporarily the intermittent electrical actuation of the ignition means or spark plug for the combustion chamber. The interruption lasts for the time the chamber is at the unsafe temperature. When the chamber returns to a safe temperature, the switch automatically serves to reinstate the intermittent electrical actuation of the spark means for it. Additionally, however, a separate manually-operated switch permits. negation of the effect of the automatic interruption so as to reinstate spark ignition even when the individual combustion chamber is at the unsafe temperature.

electrical actuation of the ignition means for the specific over-heated chamber.

12 Claims, 7 Drawing Figures PATENTEDSEFZSIBH 3,760,781 sum 1 org 24 n INVENTOR.

' gLEN R. BOLDT H6. 4 H 5 Mfi/ A TTORNEY PATENIEU 3.760.781

SHEET 2 BF 2 INVENTOR. GLE/V R. BOLDT WLM ATTORNEY ENGINE SAFETY SYSTEM HAVING SAFETY ASSEMBLY INDENTIFIABLY OPERABLE FOR EACH COMBUSTION CHAMBER This invention relates to'a safety system for internal combustion engines, and more particularly, to an internal combustion engine having at least two combustion chambers, with each such chamber equipped with a safety assembly operable independently of the others. The invention is especially directed to mobile vehicles, particularly snowmobiles, equipped with an instrument panel and powered by an internal combustion engine protected by the safety system hereof.

Although the invention is useful in connection with internal combustion engines of a variety of types, it is especially useful and important in connection with snowmobile vehicles. Such vehicles are normally powered by air-cooled engines. They are widely used in racing and other rigorous cross-country conditions. The type of use to which they are put causes the individual combustion chambers of cylinders of the air-cooled engines to rise and lower in temperatures relatively rapidly and differentially; that is, one cylinder of the aircooled engine may rise much more rapidly in temperature than another or other cylinders of it. Such a resulr is not common under racing conditions and can be quite common under other rigorous use conditions. Contributing factors may be a difference in lubrication for the different cylinders, or a difference in heat dissipation through the fins of the air-cooled engine. In any event, a serious problem exists with respect to blowing pistons in individual cylinders of snowmobile engines when an individual cylinder reaches excessive temperatures; and it is to a solution for that particular problem that this invention is especially directed.

The invention provides alternative solutions in terms of details; and in this respect the preferred embodiment of the invention is that which permits the desired safety features without requiring the operator to remove his eyes from the terrain ahead even for an instant. Optionally, the invention includes instrument panel warning indicia which the operator may check visually at moments convenient and safe for him so to do.

The invention is applicable to mobile vehicles powered by internal combustion engines having at least two and preferably more than two combustion chambers. Ordinarily these combustion chambers are cylindrical chambers with reciprocating pistons therein. Each such chamber has associated with it an inlet for combustibles (fuel and oxygen), an ignition means (such as a spark plug) intermittently electrically actuated to ignite combustibles within the chamber, an exhaust outlet for products of combustion from the chamber, and a safety assembly according to this invention. Each such safety assembly operates independently of the safety assembly for each and every other combustion chamber of the engine.

Each safety assembly comprises a temperature sensor which is so mounted as to sense an unsafe operating temperature for the specific combustion chamber with which it is associated. Mounting of the sensor is preferably at the exhaust port or conduit for the combustion chamber, or alternately at the base of the spark plug for it. Responsive means is actuated by the temperature sensor when the specific combustion chamber reaches the unsafe operating temperature. Such unsafe operating temperatures will vary amongst the different types of engines, depending largely upon the specific material of the cylinder walls (which usually is steel), the material of pistons therein (ordinarily lighter weight alloys which melt at temperatures lower than the cylinder walls) and the arrangement and type of air fins for air cooling.

Each safety assembly for each combustion chamber or cylinder is equipped with an interrupting means for temporarily interrupting the intermittent electrical actuation of the ignition means for that combustion chamber during the time that individual or specific combustion chamber is at an unsafe operating temperature. The interrupting means for any one combustion chamber of the total engine is operable without terminating or interrupting the ignition means for combustibles in other combustion chambers of the engine.

In the preferred embodiment for snowmobiles, the interrupting means is automatically actuated by a responsive switch means which controls the interruption and is actuated automatically by the sensor when the unsafe operating temperatures are reached. A further feature of this preferred embodiment is that of separate manually operated switch means for negating the effect of the automatic interruption or terminating of the intermittent electrical actuation of ignition means for the combustion chamber which reaches unsafe operating temperatures. Thus, in a race or emergency, this manually operated switch may be used to reinstate the intermittent electrical actuation of the ignition means for the specific combustion chamber at the excessive temperatures, hopefully with the result that the dangerous condition will soon pass or at least not result in immediate blowing of the piston in the over-heated chamber.

In an alternate embodiment of the invention, the temperature sensor automatically actuates a responsive warning means when the unsafe operating temperatures is reached. The warning may illuminate an instrument panel light for the specific over-heated combustion chamber, or cause an audible sound such as a buzzer for that chamber, or effect both such alerting means. Thereafter, manually operated switch means (preferably on the .instrument panel) may be employed to terminate or interrupt temporarily the intermittent electrical actuation of the ignition means for the overheated chamber'without total loss of power. A total power loss might in some instances prove more hazardous to life and limb than any possible danger associated with blowing a piston.

Preferably both major embodiments of the invention include alerting means such as visual or audible indicators. The color of the visual indicator or warning light for each combustion chamber ideally is distinctive and different from the others. Where audible indicators are solely used, or used in conjunction with warning lights, the audible indicator for each chamber ideally is distinctive either by pitch or volume or intermittent performance or otherwise. Thus an operator is given intelligence as to the specific chamber which is in a problem condition.

The invention will further be described by reference to a drawing, made a part hereof, wherein:

FIG. 1 is a schematic circuit diagram, including schematically shown elements for an internal combustion engine, illustrating the preferred embodiment of the invention;

FIG. 2 is a schematic circuit diagram, including schematically shown engine elements, illustrating an alternate embodiment of the invention;

FIG. 3 is a fragmentary circuit diagram to illustrate the circuit for a still further alternate embodiment of the invention;

FIG. 4 is a schematically illustrated spark plug and associated temperature sensor; 7

FIG. 5 is a schematic cross section through a cylinder wall and exhaust port therefrom including a tempera ture sensor mounted for pick up of the exhaust temperature condition;

FIG. 6 is a diagrammatic cross-sectional showing of an air-cooled internal combustion engine (partially broken away), particularly illustrating two combustion chambers and the inlets and outlets associated therewith; and

FIG. 7 is a diagrammatic showing of a snowmobile vehicle (partially broken away), powered by an aircooled internal combustion engine.

FIGS. 6 and 7 show well-known matters such as a snowmobile 38, an instrument panel 39, two internal combustion chambers or cylinders 19 and 20 of an aircooled internal combustion engine 40, reciprocating pistons 41 and 42 in the combustion chambers, a valve controlled inlet 43 and 44 for each chamber for entry of combustibles therein, and a valve controlled exhaust outlet 45 and 46 for each chamber. Ignition means 17 and 18, plus a temperature sensors 21 and 22, are included in the showing of FIG. 6 for each chamber 19 and 20 to aid in keying the illustration of FIG. 6 to the main showing of the invention in FIGS. 1 through 5, inclusive. Many obvious known details of engines can be visualized conveniently and readily without the aid of a drawing. FIGS. 1 through 5, inclusive, of the drawing are limited to basic elements for teaching the invention, and the relationships of those elements.

As a starting point in explaining the invention in light of FIGS. 1-5 of the drawing, a reference to conventional well understood elements will first be made. In both F IGS. 1 and 2, a conventional primary ignition circuit is illustrated by a battery 10, an ignition coil 11, and a breaker or breaker point system 12. As is well understood, a secondary circuit through conductor 13 from the secondary winding of the coil 11 goes to a distributor 14 or equivalent means for sequential selective distribution of an electrical pulse (from the coil 11 or equivalent) through discreet conductors 15 and 16 to individual ignition means such as spark plugs 17 and 18 for cylinders 19 and 20 of an internal combustion engine. Only two combustion chambers or cylinders are illustrated in the drawing for the sake of simplicity. The arrangement of elements described thus far, as well as the use of equivalent or alternate means for sequential distribution of the electrical pulse to the ignition means or spark plugs 17 and 18, is well known. The important feature is that each spark plug is provided with a source which intermittently and according to prearranged timing serves to ignite combustibles in the cylinder with which it is associated.

Each combustion chamber of the engine is equipped with a safety assembly; and each safety assembly includes a temperature sensor 21 and 22. The sensor 21 or 22 is mounted to sense the operating temperature for the specific combustion chamber 19 and 20, respectively, of the internal combustion engine with which the sensor is associated. Specifically, as illustrated in FIGS.

4 and 5, the sensor 21 or 22 is, as a practical matter, either mounted to receive conducted temperature through a conductor 23 from a brass or copper bushing or gasket 24 at the base of the spark plug 25 for the individual combustion chamber (as in FIG. 4), or is mounted to receive conducted heat directly from the exhaust port or conduit 26 for products of combustion leaving the specific combustion chamber (the wall 27 of which is shown in FIG. 5) prior to the time those products of combustion enter any optional exhaust manifold or other conduit system for conveying them away. Optionally, the sensor might be placed in a special recess in the wall of a combustion chamber or in still other locations effective to permit temperature sensing of individual combustion chambers. Further, the sensor may itself be somewhat remote from the chamber, provided it is effectively coupled with it for sensing its temperature. Where the sensor is displaced from the immediate area of the combustion chamber, but is coupled with it, as in the case of the spark plug arrangement in FIG. 4, the sensor should be adjusted to respond at relatively lower temperatures than a sensor mounted in the exhaust port or conduit for the combustion chamber. Further, unsafe temperatures taken by conduction from a brass gasket 24 for the spark plug 25 may be as low as 400 or 450 F. or possibly 500 F., whereas unsafe temperature readings at the exhaust port normally will be relatively much higher, such as around l,000 F., or even 1,400 F., or more.

A variety of specific known temperature sensors may be employed. Popular types are made of a bimetallic strip or a coil which curves or unwinds (respectively) as temperature rises. The end of the strip or coil of bimetallic material either makes or breaks contact with a conductor at the level of temperature predetermined to be in the unsafe range for a specific type of internal combustion engine or the pistons and cylinders thereof. Any suitable sensor capable of either making or breaking an electrical connection at a predetermined unsafe operating temperature may be employed, although the specific features of circuitry for the safety assembly must be adjusted consistent with either the making or breaking of contact.

In the embodiment illustrated in FIG. 1, the sensors 21 and 22 are equipped with responsive switch means of the normally open or broken circuit type; and this switch (or connector points) close to complete a circuit at the unsafe operating temperature. This automatically occurs when the unsafe temperature is reached, and is caused by the bimetallic sensor element disproportionately expanding to place an end thereof in electrical contact with a fixed electrical contact disk. Such sensors and switch combinations are well known (see, for example, disclosure in U.S. Pat. No. 3,421,489).

Because manually operated switches 28 and 29 (suitably in a bank of manually operated switches on an instrument panel) is in the normally closed position as the engine is ordinarily operated, the automatic closing of the responsive switch means associated with sensors 21 and 22 in FIG. 1 (at unsafe operating temperatures for the specific combustion chamber each is sensing) will short out or ground the electrical pulses from distributor 14 to the respective spark plug 17 or 18 for the chamber at unsafe temperatures. The shorting or grounding of the pulse for one spark plug by the safety assembly associated with it does not interfer with the electrical pulse to the other spark plugs.

Desirably the manual switches 28 and 29 are in a bank of switches on an instrument panel of the vehicle. Each switch in the bank is desirably associated with a panel light such as 30 and 31, respectively, so that an operator can by visual inspection determine the specific switch 28 or 29 'which can (where desired, as in a race) be shifted to an open condition to resinstate the operation of the combustion chamber which is at unsafe temperature. By shifting that switch 28 or 29 to open it, the operator can thus reinstate intermittent electrical actuation of the ignition means 17 or 18 for the chamber. Further, by flipping the switch 28 or 29 back to closed, he can periodically check to determine whether the unsafe temperature persists.

Either in combination with lights 30 and 31, or in substitution for such lights, special different audible warning sounds, each characteristic for a predetermined manual switch 28 or29, may be employed.

In FIG. 3, an embodiment is illustrated where the sensor 32 includes a responsive switch means of the normally closed type, opening when unsafe operating temperatures are reached and thereby, because of the illustrated circuitry in FIG. 3, interrupting the electrical ignition pulse from distributor 14 to spark plug 17. A manually operated by-pass switch 33 is used for reinstating the connection from distributor 14 to spark plug 17 should the operator determine that the risk of a piston blow out is worth taking for a short period of time.

In the embodiment illustrated in FIG. 2, the operator is warned of a dangerous temperature condition if it arises for a specific combustion chamber, but must take manual action in order to stop continued combustion in the chamber which is at unsafe temperatures. The sensors 21 and 22 in FIG. 2 include or comprise normally open switches which close at the unsafe temperatures. Upon closing, they automatically electrically actuate a warning means 34 or 35, which may comprise either or both a visual (light) or audible (buzzer) means. Warning means 34 and 35 are suitably in a bank of such means on an instrument panel; and with each or adjacent to each should be a manually operated switch 36 and 37 corresponding to or applicable to the safety system for the combustion chamber. Thus, if warning means 34 alerts the operator, he may elect, depending on his judgment, to shift switch 36 from a normally closed position (for conduction of electrical pulses from distributor 14 to spark plug 17) to an open and grounded condition and thereby interrupt temporarily the intermittent electrical actuation of the ignition spark for cylinder 19. And this is optionally possible at his discretion without losing all power; that is, without interrupting the spark ignition for combustion chamber 20 or any other combustion chambers of the engine.

As used herein, the reference to blowing pistons refers to damaging or buming the pistons as a result of overheating. Overheating causes pistons to expand so greatly that they freeze or lock-up in the cylinder, becoming damaged themselves in the process and many times also causing damage to the cylinder walls.

If desired, visual warning means such as needle heat guages could be employed for individual cylinders in practicing the teachings hereof, preferably in addition to other visual warning means; and still other variations from the preferred embodiments illustrated may be employed.

That which is claimed is:

1. An internal combustion engine having at least two combustion chambers, each said combustion chamber having associated therewith an inlet for combustibles, ignition means intermittently electrically actuated to ignite combustibles within said chamber, an exhaust outlet for products of combustion from said chamber, and a safety assembly, said safety assembly for each said combustion chamber being operable independently of the safety assembly for each and every other combustion chamber of said engine, and each said safety assembly comprising:

a. A temperature sensor mounted to sense an unsafe operating temperature for the specific combustion chamber with which said sensor is associated,

b. Responsive switch means automatically actuated by said sensor when said specific combustion chamber reaches said unsafe operating temperature, whereby said intermittent electrical actuation of said ignition means for said specific combustion chamber is interrupted during the time said specific combustion chamber is at said unsafe operating temperature, said responsive switch means being operable without interrupting the intermittent electrical actuation of the ignition means for all of the other combustion chambers of said engine, and

c. manually operated switch means for negating the effect of said responsive switch means and thereby reinstating said intermittent electrical actuation of said ignition means for said specific combustion chamber, said manually operable switch means for each said combustion chamber safety assembly being identifiably distinct from the manually operated switch means for every other said combustion chamber safety assembly.

2. The engine of claim 1 wherein the mounting of said temperature sensor is such as to sense the temperature at the exhaust outlet for said specific combustion chamber.

3. The engine of claim 1 wherein the mounting of said temperature sensor is such as to sense the temperature at the base of the ignition means for said specific combustion chamber.

4. The engine of claim 1 wherein said safety assembly comprises a visual indicator automatically actuated bysaid sensor when said specific combustion chamber reaches said unsafe operating temperature, said visual indicator of each said combustion chamber safety assembly being identifiably distinct from the visual indicator for every other said combustion chamber safety assembly.

5. The engine of claim 1 wherein said safety assembly comprises an audible indicator automatically actuated by said sensor when said specific combustion chamber reaches said unsafe operating temperature, said audible indicator of each said combustion chamber safety assembly being identifiably distinct from the audible indicator for every other said combustion chamber safety assembly.

6. A mobile vehicle powered by an air-cooled internal combustion engine satisfying the requirements of claim 1.

7. An internal combustion engine having at least two combustion chambers, each said combustion chamber having associated therewith an inlet for combustibles, ignition means intermittently electrically actuated to ignite combustibles within said chamber, an exhaust outlet for products of combustion from said chamber,

and a safety assembly, said safety assembly for each said combustion chamber being operable independently of the safety assembly for each and every other combustion chamber of said engine, and each said safety assembly comprising:

a. A temperature sensor mounted to sense an unsafe operating temperature for the specific combustion chamber with which said sensor is associated,

b. Responsive warning means automatically actuated by said sensor when said specific combustion chamber reaches said unsafe operating temperature, said responsive warning means being operable without interrupting the intermittent electrical actuation of said ignition means for said specific combustion chamber, and

c. manually operated switch means for temporarily interrupting intermittent electrical actuation of said ignition means for said specific combustion chamber during the time said specific combustion chamber is at said unsafe operating temperature, said switch means being operable without interrupting the intermittent electrical actuation of the ignition means for all of the other combustion chambers of said engine.

8. The engine of claim 7 wherein the mounting of said temperature sensor is such as to sense the temperature at the exhaust outlet for said specific combustion chamber.

9. The engine of claim 7 wherein the mounting of said temperature sensor is such as to sense the temperature at the base of the ignition means for said specific combustion chamber.

10. The engine of claim 7 wherein said responsive warning means comprises a visual indicator for alerting an operator.

11. The engine of claim 7 wherein said responsive warning means comprises an audible indicator for alerting an operator.

12. A mobile vehicle powered by an air cooled internal combustion engine satisfying the requirements of claim 7.

, UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No; 3,760,781. Dated September 5, 197,3

Inventor(s) Glen R. Boldt It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 25, r'esulr" should read result Column 1, line 26, "common" should read uncommon Signed and sealed this 19th day of MarchlQTLr.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM P640150 USCOMM-DC 6O376-P69 U.S. GOVERNMENT PRINTING OFFICE I9 9 0-366-33, 

1. An internal combustion engine having at least two combustion chambers, each said combustion chamber having associated therewith an inlet for combustibleS, ignition means intermittently electrically actuated to ignite combustibles within said chamber, an exhaust outlet for products of combustion from said chamber, and a safety assembly, said safety assembly for each said combustion chamber being operable independently of the safety assembly for each and every other combustion chamber of said engine, and each said safety assembly comprising: a. A temperature sensor mounted to sense an unsafe operating temperature for the specific combustion chamber with which said sensor is associated, b. Responsive switch means automatically actuated by said sensor when said specific combustion chamber reaches said unsafe operating temperature, whereby said intermittent electrical actuation of said ignition means for said specific combustion chamber is interrupted during the time said specific combustion chamber is at said unsafe operating temperature, said responsive switch means being operable without interrupting the intermittent electrical actuation of the ignition means for all of the other combustion chambers of said engine, and c. manually operated switch means for negating the effect of said responsive switch means and thereby reinstating said intermittent electrical actuation of said ignition means for said specific combustion chamber, said manually operable switch means for each said combustion chamber safety assembly being identifiably distinct from the manually operated switch means for every other said combustion chamber safety assembly.
 2. The engine of claim 1 wherein the mounting of said temperature sensor is such as to sense the temperature at the exhaust outlet for said specific combustion chamber.
 3. The engine of claim 1 wherein the mounting of said temperature sensor is such as to sense the temperature at the base of the ignition means for said specific combustion chamber.
 4. The engine of claim 1 wherein said safety assembly comprises a visual indicator automatically actuated by said sensor when said specific combustion chamber reaches said unsafe operating temperature, said visual indicator of each said combustion chamber safety assembly being identifiably distinct from the visual indicator for every other said combustion chamber safety assembly.
 5. The engine of claim 1 wherein said safety assembly comprises an audible indicator automatically actuated by said sensor when said specific combustion chamber reaches said unsafe operating temperature, said audible indicator of each said combustion chamber safety assembly being identifiably distinct from the audible indicator for every other said combustion chamber safety assembly.
 6. A mobile vehicle powered by an air-cooled internal combustion engine satisfying the requirements of claim
 1. 7. An internal combustion engine having at least two combustion chambers, each said combustion chamber having associated therewith an inlet for combustibles, ignition means intermittently electrically actuated to ignite combustibles within said chamber, an exhaust outlet for products of combustion from said chamber, and a safety assembly, said safety assembly for each said combustion chamber being operable independently of the safety assembly for each and every other combustion chamber of said engine, and each said safety assembly comprising: a. A temperature sensor mounted to sense an unsafe operating temperature for the specific combustion chamber with which said sensor is associated, b. Responsive warning means automatically actuated by said sensor when said specific combustion chamber reaches said unsafe operating temperature, said responsive warning means being operable without interrupting the intermittent electrical actuation of said ignition means for said specific combustion chamber, and c. manually operated switch means for temporarily interrupting intermittent electrical actuation of said ignition means for said specific combustion chamber during the time said specific combustion chamber is at said unsafe operating temperature, Said switch means being operable without interrupting the intermittent electrical actuation of the ignition means for all of the other combustion chambers of said engine.
 8. The engine of claim 7 wherein the mounting of said temperature sensor is such as to sense the temperature at the exhaust outlet for said specific combustion chamber.
 9. The engine of claim 7 wherein the mounting of said temperature sensor is such as to sense the temperature at the base of the ignition means for said specific combustion chamber.
 10. The engine of claim 7 wherein said responsive warning means comprises a visual indicator for alerting an operator.
 11. The engine of claim 7 wherein said responsive warning means comprises an audible indicator for alerting an operator.
 12. A mobile vehicle powered by an air cooled internal combustion engine satisfying the requirements of claim
 7. 